michigan state university Brooke n. mAcnAmArA case western reserve university neil chArness florida state university dAvid Z. hAmBrick michigan state university how important are training and other forms of domain-relevant experience in predicting individual differences in expertise?to answer this question, we used structural equation modeling to reanalyze data from a study of chess by charness, tuffiash, krampe, reingold, and vasyukova (2005). latent variables reflecting serious chess activity and formal instruction, along with a manifest variable indexing serious starting age, accounted for 63% of the variance in peak rating. serious starting age had a significant negative effect on peak rating (β = -.15), even after we controlled for domain-specific experience, indicating an advantage for starting earlier. we also tested the prediction that formal instruction increases the effectiveness of serious study (ericsson & charness, 1994) using moderated regression. this claim was not supported. overall, the results affirm that serious study and other forms of domain-specific experience are important pieces of the expertise puzzle, but other factors must matter too.supplemental materials are available at https://www.press.uillinois.edu/journals/ajp/media/ chess_skill keywords: chess, expertise, deliberate practice, starting age, formal instruction How important are training and other forms of experience in accounting for individual differences in skill in complex domains? This question is the subject of vigorous debate in the scientific literature on expertise. A recent series of studies used meta-analysis to investigate this question. In the first meta-analysis, previous studies from two of the most widely researched domains of expertise, chess and music, were reanalyzed. After correction for measurement error (i.e., unreliability), estimates of deliberate practice (i.e., activities specifically designed to improve the current level of performance; Ericsson, Krampe, & Tesch-Römer, 1993) accounted for 34% of the variance in chess expertise and 30% of